1. Field of the Invention
This invention relates to a polyolefin composition having improved secondary processing properties such as paintability (coating fitness), printability and adherable property as well as good physical properties and particularly, a polyolefin composition containing polyamide and having a low melt temperature.
2. Prior Art
Polyolefins have neither polar group nor active group showing reactivity in their molecular structure and are poor in a solubility in solvents, therefore they are excellent in resistance to chemicals and solvents, but they are inferior in such secondary processing properties as paintability, printability and adherable property. Various methods have been proposed to improve these secondary processing properties of polyolefins.
In printing, a flame-treatment or a corona discharge treatment is generally employed, but these techniques involve the disadvantage that the shape of the moldings which are processed is restricted.
In adhesion, a chemical surface treatment is known where the surface of a molding is oxidized with a chromium acid-sulfuric acid mixed solution; however, in this method there are disadvantages that dangerous chemicals are used, operations are complicated and the treated surface lose lustre. Further, local treatment is difficult.
In coating, several methods are known, that is, a plasma treatment at lower temperature, graftpolymerizing method wherein a monomer having a functional group is graftpolymerized onto the surface of molded articles, or the like, but these methods are useless from the standpoint of practical use.
And various primer coating methods have been proposed, but they are inconvenient because the primer is expensive and requires baking, or because applicable paints on to the primer coating are restricted.
Also it has been tried to copolymerize an olefin with a comonomer having a functional group, but the resulting copolymer is not good in paintability, although it is good in melt adherable property to metal.
The inventors of this invention have found that a surface treatment with a chlorinated polyolefin solution improves paintability of molded articles of a blended polymer consisting of polyolefin, polystyrene and thermoplastic elastomer (see Japanese Patent Publication Nos. 46662/1980 and 50171/1984). The blended polymer maintains its practical performance based on the polyolefin but is deteriorated in such properties as rigidity or stiffness, surface hardness, resistance to heat deformation, and surface gloss of molded articles. Decreases in rigidity or stiffness and resistance to heat deformation can be made up for by the addition of filler but decreases in surface hardness, particularly scratch resistance and surface gloss, cannot be made up for by any means.
One of the inventors of this invention has found that a surface treatment with a solution of chlorinated polyolefin and a monomer having carbon-carbon double bond and a glycidyl group in a mixed solvent of terpenic solvent and aromatic or chlorinated hydrocarbon solvent remarkably improves the paintability of molded articles of the blended polymer above described as compared with the solution containing only chlorinated polyolefin. Namely, the surfaces of molded articles thus treated become receptive to more kinds of paint and are more glossy in comparison to the surfaces of articles treated with the solution containing only a chlorinated polyolefin (see Japanese Patent Laid-Open Application No. 195734/1982).
However, it is useless from the standpoint of practical use to apply the treatment just mentioned above to the surface of molded articles of the blended-polymer, because the surface is less resistant to scratching and the difference in gloss between treated and untreated surface of the molded articles is striking.
The inventors of this invention have carried out studies in search of a polyolefin composition, which causes no deterioration of the physical properties of the articles and makes the surface receptive to more kinds of paint, by the treatment with the chlorinated polyolefin solution. As a result, they found that a polyolefin composition comprising polyolefin and a minor amount of polyamide dispersed therein achieves the object above mentioned.
The molding temperature of the blended polymer of the polyolefin and the polyamide has to be higher than the melting temperature of the polyamide (nylon 6: 218.degree. C., nylon 66: 259.degree. C.). This results in the following disadvantages:
(1) The blended polymer cannot be molded by blow or extrusion molding which should be carried out at a low molding temperature. PA1 (2) It is necessary to mold the blended polymer at a high temperature at which it is impossible to achieve the main object of injection molding, that is, making the cycle time shorter by low temperature molding. PA1 (3) When such a heat decomposable organic filler as woodflour is blended with the blended polymer or when the resulting blended polymer is molded, the temperature of the blended polymer should be higher than 200.degree. C. at which the filler decomposition is accelerated. The gas thus formed makes silver streaks on the surface of the molded articles which as a result are unusable as a base material for external use or coating. Further, the gas may rust the mold. PA1 (a) not less than 2 percent by weight of a monomer having at least one carbon-carbon double bond and a glycidyl group, PA1 (b) 1 to 5 percent by weight of chlorinated polyolefin, and PA1 (c) 97 percent by weight of a mixed solvent of 30 to 70 percent by weight of terpenic solvent and 70 to 30 percent by weight of aromatic or chlorinated hydrocarbon solvent. PA1 (a) not less than 2 percent by weight of the monomer having at least one carbon-carbon double bond and a glycidyl group, examples of which monomer include glycidyl allyl ether, glycidyl acrylate and glycidyl methacrylate, PA1 (b) 1 to 5 percent by weight of the chlorinated polyolefin, and PA1 (c) not more than 97 percent by weight of a mixed solvent consisting of 30 to 70 percent by weight of terpenic solvent such as -pinene, dipentene or a mixture thereof and 70 to 30 percent by weight of aromatic or chlorinated hydrocarbon solvent.